Downhole devices are often used during drilling operations which are required to engage the wall of the borehole. These borehole engaging devices are typically located along the length of the drilling string and extend radially or outwardly therefrom to engage the borehole wall to perform their specific intended function.
Such downhole borehole engaging devices include stabilizers, underreamers and anti-rotation devices. Stabilizers are typically located at various positions along the length of the drilling string to provide lateral support for the drilling string and to centralize the drilling string in the borehole. The stabilizer may be comprised of blades, pads or any other borehole engaging member capable of supporting and centralizing the drilling string, which members tend to be fixed in an extended position extending outwardly or radially from the drilling string. When using a stabilizer, it is desirable that each of the blades, pads or other borehole engaging members engage the borehole wall concurrently or simultaneously in order to support and centralize the drilling string. Thus, the size or gauge of the stabilizer is selected to be compatible with the size or gauge of the borehole in which it is to be used such that the stabilizer can perform its intended function.
Underreamers are typically utilized in the drilling string in order to expand the gauge or diameter of the borehole to a dimension which is greater then the gauge or diameter which is attainable with only a drill bit. The underreamer may be comprised of blades or any other borehole engaging member capable of reaming the borehole wall in the desired manner, which borehole engaging members preferably engage the wall such that the gauge or diameter of the borehole can be increased relatively evenly or consistently. The borehole engaging members of the underreamer may be fixed in an extended position, such as in the stabilizer, or the members may be movable between an extended position and a retracted position. The member is preferably capable of being locked in the extended position to perform the reaming function. Thus, as with the stabilizer, the size or gauge of the underreamer is selected to be compatible with the size or gauge of the borehole in which it is to be used such that the underreamer can perform its intended function.
Anti-rotation devices or rotation restraining devices are often used during drilling operations to enable a portion of the drilling string, such as a housing of a downhole motor, a rotary steerable device or system or other drilling apparatus, to resist rotation relative to the wall of the borehole. For instance, a drilling string or a drilling shaft with an attached drill bit may be rotated to perform the drilling operation, while it is desirable to resist the rotation of a housing surrounding the drilling string or drilling shaft in order to provide for or to enhance the stability and/or steerability of the drill bit.
In such applications, the drilling string or drilling shaft typically rotates within the housing while an anti-rotation device associated with the housing engages the borehole wall in order to resist the rotation of the housing. Anti-rotation or rotation restraining devices are commonly used in conjunction with downhole motor assemblies and rotary steerable drilling systems, such as that shown in U.S. Pat. No. 6,244,361 issued Jun. 12, 2001 to Comeau et. al.
A typical anti-rotation device is comprised of a number of rotation restraining members such as blades, pads, rollers or pistons which are arranged about the circumference of the housing and protrude therefrom in order to engage the borehole wall. In order to function in the desired manner and inhibit the rotation of the housing, at least one of the rotation restraining members must engage the borehole wall. These members may be movable between extended and retracted positions to facilitate movement of the anti-rotation device through the borehole. Further, as with the stabilizer and the underreamer, the size or gauge of the housing and the anti-rotation device, including the protruding rotation restraining members, are selected to be compatible with the size or gauge of the borehole in which the anti-rotation device is to be used such that the anti-rotation device can perform its intended function.
More particularly, with respect to the anti-rotation device, the housing typically has a fixed diameter. The rotation restraining members are affixed or fitted within the housing and typically have a limited range of radial movement relative to the housing. Thus, the anti-rotation device has a pre-determined or relatively fixed gauge, size or dimension suitable for use within one selected or desired gauge of borehole. In other words, the drilling apparatus, including the anti-rotation device affixed or fitted within the housing thereof, must be assembled for each specific size or gauge of borehole in which it is to be used. For instance, to utilize the drilling apparatus in boreholes having different gauges or within a single borehole having a varying gauge, the housing and the anti-rotation device affixed thereto must be selected to have a size or configuration compatible for insertion in each differing borehole gauge. Accordingly, a different drilling apparatus having a different configuration must be provided for each borehole gauge or the drilling apparatus must be substantially disassembled and re-assembled to be suitable for each borehole gauge.
As a result, there is a need for a variable gauge drilling apparatus for use in drilling operations. Further, there is a need for a variable gauge drilling apparatus comprised of a borehole engaging device, such as a stabilizer, an underreamer or an anti-rotation device, in which the gauge of the drilling apparatus can be relatively easily varied to permit its use in a range of borehole sizes or gauges such that the borehole engaging device engages the borehole wall to perform its intended function.